Uh -- you missed a few: from the late 1950's through the 1980's for example, you have (NOT an exhaustive list) Herb Elliott, Jim Ryun Dave Wottle, Pekka Vasala, Rick Wohlhuter, Steve Ovett, Steve Cram, Sebastian Coe, Joaquim Cruz, Said Aouita (yes, he ran the 800 too -- Olympic bronze medalist in 1988), and Peter Elliott -- all global medalists at -- at least -- one of the two and among the best in the world at the other. It is true that some more recent champions (e.g., El Guerrouj, Ingebrigtsen) have been more 1500-5000 types, but you still have had Ngeny, Makhloufi, Kiprop, Wightman, and many others who were 1500 globla medalists and still veyr, very competitive globally at 800.
There's less history on the women's side (1500 wasn't added to the Olympics until 1972), but you still have Tatyana Kazankina, Kelly Holmes, and Svetlana Masterkova (all of who won 800-1500 doubles at the Olympics, I think), plus Mary Decker (1:56.9 in 1985, when she also ranked T&FN world #1 at 1500 and 3000), Kim Gallagher Keely Hodgkinson, Jemma Reekie. All but Reekie have been global medalists at at least one of the two.
In addition to the evidence above, and as I pointed out in previous posts, Mu really is unique in our time. She was among the best in the U.S. in HS at distances from 200 through 1500 meters. So I was not surprised to see her do so well in the 1500 at USATF and I don't think whatever 1500 training she has done would have made her uncompetitive in the 800.